People with DO meters

[tatuvaaj]

Hello!

Could some one with a DO meter tell what kind of DO levels they measure from their reef aquarium both during night and day? Also, if you could report your salinity, temperature and sand depth I would be most thankful ! :)

TIA !

[Randy Holmes-Farley]

I'm interested too, although I've never taken such measurements.

Do you have any data of your own?

[tatuvaaj]

Randy,

No, I don't have a DO meter yet. I've been thinking about buying one for a long time. If the data people report (hopefully!) looks interesting enough I'll buy one ;)

[Boomer]

tatu

I don't have one either, but a proper O2 meter is 100's of dollars and are corrected for Salinity and atmospheric pressure. You may want to try the HACH Digital Titrator for $ 140. Test O2 down to 0.02 mg / l. I have one :D. No, I never ran the test you want :mad: You will be suprised what you get though. Many people don't have as much as they think :D

[tatuvaaj]

Originally posted by Boomer
I don't have one either, but a proper O2 meter is 100's of dollars and are corrected for Salinity and atmospheric pressure. You may want to try the HACH Digital Titrator for $ 140. Test O2 down to 0.02 mg / l. I have one :D.
Thanks for the tip! :thumbsup: That sounds reasonable.
No, I never ran the test you want :mad: You will be suprised what you get though. Many people don't have as much as they think :D
Yes, that's what I'm afraid of :) For example, Ascidians are known to lower their pumping rates when oxygen levels drop enough.

[Boomer]

Ascidians

One of my favorite groups :D Got a coupld of books on them

[Randy Holmes-Farley]

I'll check and see if I can find one to try. This sounds interesting. :)

[Habib]

Tatu,

We have a WTW O2 meter + probe.

Can't remember what we paid.

IME an O2 measurement is not so interesting unless one want's to experiment. ;)

Addition of food and use of organic based calcium supplements will consume oxygen.

[Randy Holmes-Farley]

One thing I'd like to test is how well O2 remains when I have a power failure and I'm left with just backup powerheads on a UPS.

[rsman]

try the HACH Digital Titrator for $ 140 I have that at probibly boomers previous recomendation, and I borrowed a DO meter i played around with them on a number of tanks just for kicks

its cool, but I didnt have a reference point for my reef, I use it on my cultures instead :D

the power loss issue was a serious concern when I was playing the backup powerhead will work SOOO much better if you hook up a venturi to it, you can hook it up so that in normal operation its submerged, but when the waterlevel lowers a tad when the return is cut the air hose sticks out of the water. the best results I found was a battery powered air pump hooked up to a small airlift with a 90 elbo. though you might need more than 1 the cost and runtime is offset by the cost of a UPS and powerhead.

[Randy Holmes-Farley]

you can hook it up so that in normal operation its submerged, but when the waterlevel lowers a tad when the return is cut the air hose sticks out of the water.

Nice suggestion. Thanks. :)

[rsman]

ooh yea I forgot put an airline T on the end. itll keep that mini whirlpool thing down and keep things from blocking the input.

[Randy Holmes-Farley]

:thumbsup:

Thanks. :)

[Habib]

Originally posted by Randy Holmes-Farley
One thing I'd like to test is how well O2 remains when I have a power failure and I'm left with just backup powerheads on a UPS.

Sounds like a nice experiment. :)

I have a feeling that water movement might be far more important than the O2 concentration in the bulk of the water.

If there is not enough watermovement or not at all then the boundary layer around the corals will become (much) thicker and reduce the oxygen uptake rate and removal of excreted substances.

[Boomer]

Hab

You're back, missed you :D

[Bryan]

http://www.canreef.com/phpBB2/viewtopic.php?t=9942

[tatuvaaj]

Bryan,

Thanks a lot for the link! Very interesting information.

I'm somewhat surprised to see such a huge drop in O2 concentration during night, a drop to 50% from the highest value can very well have impact on at least some animals' health.

It seems like his tank doesn't have the best possible aeration so it would be interesting to see if the photosynthesis has such a huge impact on DO in tanks with a overflow and a skimmer.

[tatuvaaj]

Boomer et. al,

What do you think about the American Marine Pinpoint Oxygen Monitor ?

[beaslbob]

Please don't tell my wife there is actually a do meter.

[Boomer]

Tatu

I have some serious issues with it. First, nowhere on their website is there any mention for seawater. A DO probe needs to be corrected for seawater or at least have a table for the correction, like YSI has on there less expensive meter. Second, I see nothing on correction for barometric pressure. Some of the cheaper meters have one for altitude ( a cheap cheat method) but altitude does not always mean an equal barometric pressure across the board as you go up or down in elevation. Barometric pressure is always changing, a home barometer will show you that and it is that value what should be used as the dial in on a good O2 meter, not altitude. Some good inexpensive meters have all the corrections on a table or plotted graph but I see no mention of either for this meter.

[Boomer]

Bob, what is your phone number, I need to talk to your wife :D I have one all picked out for her, it is only grand or so, with all the Acc :lol: Tell the wife to come to the PC for a lookzee. And it is waterproof :D



http://www.ysi.com/extranet/EPGKL.nsf/447554deba0f52f2852569f500696b21/a20cd72a0f57630185256a240066ef87/P_DocBody/0.9DE!OpenElement&FieldElemFormat=jpg

[tatuvaaj]

Boomer,

Thanks again!

I might be completely lost here but wouldn't all those variables affect the saturation reading only and not the actual mg/l reading?

I think I'll get the HACH kit as you recommended. Anyone know a good online shop in EU for HACH products?

[Boomer]

I might be completely lost here but wouldn't all those variables affect the saturation reading only and not the actual mg/l reading?

No, the meters even do saturation in %. At a measured salinity, temp and barometric pressure you can mathematically calculate saturation, just as the meter
does :D

S´= S x P´/ 29.92 - ( C X F)

To make it easier for you for seawater the value from the calculator below is..... x mg / O2 = 100% saturation :D


http://www.aquanic.org/images/tools/oxygen.htm

I have two more but they are for FW:mad:

[Habib]

Randy:

This might be an interesting and useful article for the experiment you are mentioning.

http://www.biol.sc.edu/~helmuthlab/classes/corals/Articles/GardellaEdmunds99.pdf

[Boomer]

Hab, nice piece:thumbsup:

[Randy Holmes-Farley]

That is interesting. THanks. :)

Unfortunately, I struck out finding a DO meter laying around. :lol:

[tatuvaaj]

Habib,

Thanks for the link !

edited: you don't happen to have anything about the pumping rate of sponges and tunicates vs. DO levels do you? :D

[Habib]

PO4 and tunicates I probably have but not sure aboutr DO will have a look.

[Greg Hiller]

>Unfortunately, I struck out finding a DO meter laying around<

Ha...not me!! Trouble is, most of our meters are intergral to the bioreactor monitors. I've been meaning to do this for quite some time. We commonly calibrate our DO probes for bioreactors in % of airsat. This calibration in a tank should be a easy, just take a small volume of tank water, kept at tank temp, and bubble the hell out of it for a few minutes, then set the meter at 100%.

Now...if I could just find an ICP to look for contaminants in my magnesium chloride :) ....hint...hint ;)

Randy,

Are your pink skunks breeding?..on the tile?...I have rotifers coming out my ears. I was all set to raise my maroons, and the eggs fell off the tile for some strange reason.

[Randy Holmes-Farley]

No eggs on tiles yet.

[Habib]

Originally posted by Randy Holmes-Farley
One thing I'd like to test is how well O2 remains when I have a power failure and I'm left with just backup powerheads on a UPS.


Unfortunately, I struck out finding a DO meter laying around.

:D

We have a O2 meter and pulling out some plugs is not that difficult.

If it has an effect then the very good suggestion of rsman should be tested. His idea and logic is extremely good and should be made known to as many reefers as possible.

BTW I'm just thinking uploud. :)

[rsman]

Im not a chemist and I think everyone knows it :D but just in case IM NOT A CHEMIST :bounce1:

when I was playing with a DO meter I was playing around with the ICRS that the people at Reed mariculture have nicely publicly given out. their first setup and my first setup both had some issues, in that you remove the rotifers from the culture water to filter them and at some points the oxygen sats would drop *Real low* like <5% killing things :( at that time I borrowed one (ok well stole with the intent to return :D and I did return it. :D ) and played around, a problem I noticed in the post by greg seemed to be that he was going to calibrate at 100% by airating SW, this doesnt work so well as you can pass 100% fairly easily. Trying to remember when I did this, it was probibly more than 2 years ago that I did most of this. I tested my reef, and the powerhead mentoned its a rio-180 it hides nicely at the top of the tank and the bubbles extend a good 3' away it was tested in real life when calf's grey davis droped the ball leaving lots of short poweroutages. the UPS its pluged into runs about $60 now and itll run for 24 hours no problems ive tested it by unpluging it a few times mostly just for kicks. because I was playing with my breeding setup (the ICRS) I am sure I made notes, but as it was on paper and ive got a good collection now about 7" stack, and Im very disorganized.

[Boomer]

I noticed in the post by greg seemed to be that he was going to calibrate at 100% by airating SW, this doesnt work so well as you can pass 100% fairly easily.



Yes, I would agree but there is more to it than that. First, one should not be trying to calibrate a DO meter, via aeration and assuming it is 100 %, it may be more or it may be less. Second on the link given and on the tests done by Samw and the links Samw gave all relate to limnological studies, the is the science of FW Ecology, not seawater but I guess that is Ok, at least you get an idea ;) The meter he is using is a nice meter and does correct for salinity up 50 ppt :D so I would assume the values he gave are correct. As one can see, he is nowhere near 100 % sat., from his tests, par one brief reading. I have ways stated that one would be surprised at how low their DO really is in their reef tank. Many think they are 100 %. :o 100 % sat. of NSW @ STPS = 6.772 (mg/L) and FW is 8.39 (mg/L)

[Greg Hiller]

I'm sorry, I don't follow. You are saying that if I take a small volume of tank water (no critters in it), bubble room air into the water at tank temp and atmospheric pressure, and wait for the O2 level to come to equilibrium, I am not at 100% of air sat? This is 100% of air sat by definition seems to me. How can you 'pass' this number without using pressure, pure O2, or having some organism excreting O2?

FWIW, this is how (when we want to be particularly accurate) we calibrate our O2 probes in bioreactors. Have I been doing it wrong the last 15 years?

[Boomer]

Greg

How do you know it is not at 99 % or 105 %, when you calibrate ? When do you determine and how do you know when it is at equilbrium and it is 100 % ? Aren't you assuming ? You can mathamatically calculate sat.

http://www.thermidaire.on.ca/do.html

http://www.fivecreeks.org/monitor/do.html

Some things of interest

http://www.envirosim.com/products/bw32/bw32kb/17_AirExam.php

http://web.njit.edu/~hsieh/ene670/oxygen.html

[Greg Hiller]

>How do you know it is not at 99 % or 105 %, when you calibrate ?<

Very simple. I put my probe into the water. Turn the monitor on. Wait 6 hours for the polarographic probe to become completely polarized. Do an electronic zero (highly accurate, I've tested with the zeroing gel, no point in using the zeroing gel) then dial up the probe to read 100%. Keep the air stone on for another hour to see if there is any drift. This is not rocket science! This is 100% of air sat by definition. Much easier and more accurate than doing calculations that make various assumptions.

I hooked the probe up to my main tank a few hours ago. I'll take a reading tonight before the lights go off, tomorrow before they go on, and maybe I'll stop the recirc pump for a few minutes and have the %$#% scared out of me by how fast the DO falls. I have a power head put in a position to suck in air when the water level drops if the recirc pump should fail, I'll check whether that keeps the DO up also. I'll also check to see whether my battery powered air pumps are up to the task. I once before in this tank lost several large fish when the recirc pump failed. The small fish all survived (save an Anthia, makes sense really).

[Randy Holmes-Farley]

Seems reasonable to me, although I've never actually used one. :)

[Boomer]

Greg

:thumbsup:

[Greg Hiller]

Well, I calibrated mine as mentioned above, and checked the calibration several times during the later measurements, little or no drift. Seemed to work okay. I measured the DO before the lights came on, about 92-95% of air sat. After the VHO's came on for an hour or so it was about 100%. After the MH's were on for a few hours it topped off at about 108% of air sat.

For an early morning reading, I shut off all the pumps in the tank and waited about 20 minutes (before lights were on), and I did not see much of a drop in DO, maybe a percent or two. With the pumps off I had to move the DO probe about in the water just a bit to get a good reading. Polarographic probes consume a small amount of O2 while they are functioning. Although I would have liked to get an idea as to how good my powerhead (aspirating when tank level drops after recirc pumps are turned off), and the battery backup airpumps worked, I did not want to leave the recirc pumps off any longer. Problem is many of the corals are exposed (grew to surface) to air when the recirc pump is off. Now that I think of it, I suppose I could have solved the problem by cutting off the overflow, and breaking the siphon on the return lines. Well, I need to get the probe back to work tomorrow. Perhaps I'll play again another day!

[Randy Holmes-Farley]

Interesting! Thanks for the info Greg. :)

[Boomer]

Greg

the water at tank temp and atmospheric pressure

I just noticed you did not mention Salinity. Are you correcting for that ? O2 meters have to be corrected for salinity also.

[Greg Hiller]

Boomer,

>the water at tank temp and atmospheric pressure<

81 F. Sealevel.

>I just noticed you did not mention Salinity. Are you correcting for that ? O2 meters have to be corrected for salinity also.<

No need to correct due to the way the calibration is performed. My tank is at about 1.024 at the moment.

[Boomer]

Well, I'm a little lost here Greg so I called both YSI and Orion. The really didn't agree with your procedure. I read the posted answers. One answer from them was you most certainly can go over 100 % by aeration, so how are you going to know where you are at, i.e., 102 %, 105 , 99 etc.. (Orion). The other, by YSI, they weren't sure if you were correct or not buy aerating a sample and stating it can not go over 100 %. My thoughts have always been that if you heavily aerate a sample of pure water, be it FW or SW, it can go over 100 %. Rsman mentioned the same thing (below). And salinity is still a factor. Ok, for one more phone call to WTW. Same answers, the meter must be corrected for salinity. I got the same answer form them on aeration. Aeration, is a form of increasing the pressure, so saturation can go above 100 % in pure seawater, in an open beaker, at sea level, @ 82 F. And that his is not a way to be calibrating a meter in seawater.

a problem I noticed in the post by Greg seemed to be that he was going to calibrate at 100% by aerating SW, this does not work so well as you can pass 100% fairly easily

[Habib]

Boom,

Yes, you never know how fast the oxygen in the water equilibrates with the current pressure of the gas phase.

However, IMO it still was at least a relative mesurement for O2 in which a certain point was set at 100%.


FWIW our probe can be calibrated using air and there is an adjustment on the meter when measuring saltwater.

[Randy Holmes-Farley]

If we are concerned about differences between 100 and 102% of saturation, then those sorts of differences can easily be accounted for by the pressure that bubbles are under when aerating a sample. Any bubble under the surface of the water is more than 1 atm, so the oxygen partial pressure can also be higher.

[Greg Hiller]

Well...guys...this is getting a little bit silly IMO. Okay, so the air stone was about 7 inches under the water surface. 33.9 feet of head of water is equal to 14.696 PSI (if you want to be exact, lol, of course I'm not including a compensation for the density of saltwater, lol). Anyhow, I will proceed with my slightly flawed calculation: Therefore, the increase in pressure over atmospheric is 7/12/33.9 times 14.696 = 0.252 psi. 14.696 + 0.252 = 14.94

14.94/14.696 = 1.017 OMG, you are right, I'm at 101.7 percent of air sat. LOL

Anyhow, I think the point of my measurements were not to debate the best way to calibrate a DO probe, but rather to see whether I was ABOVE air sat in my tank with the lights on, mid-way through the light cycle, and to see what the readings were like at night. At a reading of 108% (with the correction above ~110%) of air sat, I think my tank was clearly above air sat. Now, the question comes, why am I above air sat? I don't doubt that the skimmer on the system (ETS 700 with a strong pump) could push the DO above air sat on its own, if there was no consumption. Clearly however there is a significant amount of O2 being generated during the daylight portion of the light cycle, presumably by photosynthesis occuring in the tank.

FWIW, this system also has an additional tank(s) in the basement plumbed to it that is on the opposite light cycle. I would imagine that the differences in day to night DO levels in the main tank would be exacerbated if it were not for this additional tank.

[Boomer]

Greg

Anyhow, I think the point of my measurements were not to debate the best way to calibrate a DO probe, but rather to see whether I was ABOVE air sat in my tank with the lights on, mid-way through the light cycle

That is fine and I understand that. I don't think it was silly at all. I was just trying to get a better understanding of the issue and that was about it :D Thanks for the detailed answer.

Clearly however there is a significant amount of O2 being generated during the daylight portion of the light cycle, presumably by photosynthesis occuring in the tank

Yes, that is what I use to see also. At times you may see O2 bubbles attached to things, usually a sign of the water being over saturated..

Did you look at this post by Bryan ?

http://www.canreef.com/phpBB2/viewtopic.php?t=9942

[Greg Hiller]

I skimmed through the post, looks like that tank is pretty low in DO in the morning, it would make me nervous I think. My guess is no overflow has some impact, I didn't look to see what type of skimmer, etc he had.

[Boomer]

it would make me nervous I think

:rollface: :rollface:

Yah, I thought the same thing. 50% is pushing it :D I could only imagine what would happen if the power or a pump went out

[Randy Holmes-Farley]

OMG, you are right

I made a lucky guess. :lol:

FWIW, I wasn't suggesting that I cared about a 2% difference. :D

[Habib]

Although the<BR>
reefs dimensions are small, the high density of organisms causes the oxygen concentration<BR>
of water flowing over it to vary by up to 50%. Where, Excess production over respiration<BR>
during daytime causes oxygen concentration to rise well above open-sea values. During<BR>
the night, respiration causes the depletion of oxygen to below open-sea values.<BR>

The above and real-time data (although don't get the O2 scale?) :

http://www.iui-eilat.ac.il/pp/rt-datastation.htm

[tatuvaaj]

Habib,

Thanks again!

That's kind of what I expected, shallow lagoons experience large DO changes. Some of the lagoons don't get much fresh sea water from the ocean.

It is interesting though that the atmospheric exchange plays (to me) surprisingly small part in the DO levels.

[Habib]

Tatu:

You're welcome.

IIRC Fossa and Nilsen have a graph of O2 (day night variation) in their book and I think I commented to Alf Nilsen about the absolute values a long time ago.


One which might prove to be useful:

The Biological Bulletin, Vol 179, Issue 1 148-158, Copyright © 1990 by Marine Biological Laboratory



Diffusion Limitation and Hyperoxic Enhancement of Oxygen Consumption in Zooxanthellate Sea Anemones, Zoanthids, and Corals
J. M. Shick
Department of Zoology and Center for Marine Studies, University of Maine, Orono, Maine 04469-0146

Depending on their size and morphology, anthozoan polyps and colonies may be diffusion-limited in their oxygen consumption, even under well-stirred, air-saturated conditions. This is indicated by an enhancement of oxygen consumption under steady-state hyperoxic conditions that simulate the levels of O2 produced photosynthetically by zooxanthellae in the hosts' tissues. Such hyperoxia in the tissues of zooxanthellate species negates the effect of the diffusive boundary layer, and increases the rate of oxygen consumption; thus, in many cases, the rate of respiration measured under normoxia in the dark may not be representative of the rate during the day when the zooxanthellae are photosynthesizing and when the supply of oxygen for respiration is in the tissues themselves, not from the environment. These results have implications in respirometric methodology and in calculating the rate of gross photosynthesis in energetic studies. The activity of cytochrome c oxidase is higher in aposymbiotic than in zooxanthellate specimens of the sea anemone Aiptasia pulchella, and this may indicate a compensation for the relative hypoxia in the tissues of the former, enhancing the delivery of oxygen to the mitochondria from the environment.

[Habib]

There is even the full article of the above version and at first sight looks quite interesting:

http://www.biolbull.org/cgi/reprint/179/1/148

[Boomer]

J. M. Shick

I have that article also in printed form, forgot about it :mad2: I have his book also, he discussesit in there.

A Functional Biology of Sea Anemones (1991)

[beaslbob]

Originally posted by tatuvaaj
Habib,

Thanks again!

That's kind of what I expected, shallow lagoons experience large DO changes. Some of the lagoons don't get much fresh sea water from the ocean.

It is interesting though that the atmospheric exchange plays (to me) surprisingly small part in the DO levels.


No suprise here. But then my experiences are different. I have seen (admitedly FW) fish at extremely high concentrations all with normal respiration in tanks with no circulation, no other filtration, just plants.

In salt I noticed the same thing only it was the addition macros to consume the carbon dioxide. Even though the consumption was only during lights on, the daytime ph rose from 7.4 to 8.4 and has stayed there. Same circulation, same tank, the only difference was the addition of the macros. The macros consuming the carbon dioxide was more effective then circulation.

[Boomer]

addition macros to consume the carbon dioxide

And what do they give off, you forgot that part Bob, O2 :D

[beaslbob]

Originally posted by Boomer
addition macros to consume the carbon dioxide

And what do they give off, you forgot that part Bob, O2 :D

Yes and that was intentional. The oxygen given off by plant action IMO does not substantially increase the dissolved oxygen in the water. And a large portion of the oxygen is given off a bubbles that simply rise to the surface without dissolving in the water.

But consuming the carbon dioxide decreases the total dissolved gasses in the water and therefore "sucks in" more air from the surface. Therefore, increasing the oxygen relative to the carbon dioxide. After the carbon dioxide from the animal life is consumed then the carbon dioxide from the air is consumed lowering the carbon dioxide below ambient values. And, of course, increasing the oxygen (and nitrogen for that matter) portion of the dissolved gasses in the water column.

[Boomer]

Pants, if you have enough of them, can impact the O2 quite a bit and bring O2 above sat.

But consuming the carbon dioxide decreases the total dissolved gasses in the water and therefore "sucks in" more air from the surface. Therefore, increasing the oxygen relative to the carbon dioxide.

No, not really. The level of O2 or CO2 have no effect on one another. Each gas has their own partial pressure and solublity rate.

After the carbon dioxide from the animal life is consumed then the carbon dioxide from the air is consumed lowering the carbon dioxide below ambient values.

The only thing that is going to lower the CO2, is plants or if the partial pressure of CO2 in the water is high enough, then CO2 will get " blown off", which either will increase the pH. This has no effect on O2 at all.

[jfinch]

Yes and that was intentional. The oxygen given off by plant action IMO does not substantially increase the dissolved oxygen in the water. And a large portion of the oxygen is given off a bubbles that simply rise to the surface without dissolving in the water.

How can you not be sure that the water is O2 saturated (from plant photosynthsis) at that point?

But consuming the carbon dioxide decreases the total dissolved gasses in the water and therefore "sucks in" more air from the surface....

The amount of CO2 in the water isn't a funtion of O2 and vice-versa. It's a funtion of temperature, salinity and partial pressure of the gas in the atmosphere.

[beaslbob]

well I never was a chemistry expert. :D

thanks for your information.

I was repeating articles a read several years ago and perhaps the memory is not all that clear.

Help me here:

As I understand it the total presure in the sum of the partial pressures.

What you are saying is that as carbon dioxide is produced or consumed it escapes or is sucked in to maintain the same partial pressure. So that no change is carbon dioxide partial pressure is possible given the same air at the air/gass interface.

And the same thing would apply to oxygen. As oxygen is consumed or produced it escapes or is sucked in to maintain the same partial pressure.

So it doesn't make any difference what we put in our tanks, the partial pressures keep the makeup of the dissolved gasses constant.

Further, that say we heat the water to boiling (0 dissolved gasses). Then we put that water under a 100% nitrogen atmosphere and allow it to cool to room temperature and equalize. the result would be a 100% partial presure of nitrogen. And that would also be the total pressure. For the sake of consistancy the room temperature pressure of the nitrogen is one atmosphere. This would result in the same amount of nitrogen in the water as water under air at one atmosphere.

Could be, been long time since chemistry and physics classes.

Whatever the mechanism, I know from experience that fish stopped breathing heavy and daytime ph rose and stabilized to 8.4 with the addition of plant life. And only with the addition of plant life.

Geesh now this is different from what i read before. And just to make it worse boomer tells the wife about a do meter. :D

[Randy Holmes-Farley]

I expect that water that has O2 bubbles in it is at or above saturation with O2. Otherwise, they would not form in the first place. All O2 coming off of algae is originally dissolved in the water, and only comes out if the water is at or above saturation. Also, if the bubbles did form somehow below saturation, they would then dissolve.

[beaslbob]

Originally posted by Randy Holmes-Farley
I expect that water that has O2 bubbles in it is at or above saturation with O2. Otherwise, they would not form in the first place. All O2 coming off of algae is originally dissolved in the water, and only comes out if the water is at or above saturation. Also, if the bubbles did form somehow below saturation, they would then dissolve.

thanks randy.

And just for the record (because I forgot to mention above) I do agree. And it does make sense.

But also is it only locally the oxygen is supersaturated? Sounds like circulation would help.

[beaslbob]

woops double post. mods please delete.

[tatuvaaj]

Just for the record, I was talking about the atmospheric exchange in nature. Well, not surprising really if the waters are calm enough at night.

BTW, the actual mechanism of gas transport from the atmosphere to water column is quite complicated (laminar boundary layers, diffusion coefficients, transfer velocities, viscosity etc. etc.) and when you insert gas injection into the picture, I just raise my hands and use reverse lighting cycle in my refugium :D :D

I'm interested in DO levels in my tank however but still haven't managed to buy the kit :rolleyes:

[tatuvaaj]

beaslbob,

You describe exactly the same I was surprised about: the data I saw suggested that the photosynthesis "controls" DO levels from 50% to supersaturation. Inside these extremes it seems that in his tank the water movement (and also differences in O2 partial pressures between the water and air) didn't have much affect. The DO levels followed pretty closely his light levels.

I always thought (ok, hoped ;) ) that water movement was enough to keep DO levels higher at night - but I was curious, that's why I started the thread.

I think we need much more data to say anything about the DO levels in reef aquariums in general ;)

[beaslbob]

I always thought (ok, hoped ) that water movement was enough to keep DO levels higher at night - but I was curious, that's why I started the thread.
And I am glad you did. Whatever the mechanism, it comes as no suprise to me. And my ph does drop to around 7.8 at night. So obviously carbon dioxide has built up.

What is important to me is that the carbon dioxide from the fish load is totally consumed and then some during the day. Whereas before I added macros to my system, the daytime ph had lowered to 7.4 and all new fish slowy deteriorated and after a couple of weeks started breathing heavy, developed white spots then died the third week. I now think they were basically sufficating.

With plant action consuming carbon dioxide and releaseing oxygen, it would make sense that lower carbon dioxide meant higher oxygen.

[Boomer]

With plant action consuming carbon dioxide and releasing oxygen, it would make sense that lower carbon dioxide meant higher oxygen.

So it doesn't make any difference what we put in our tanks, the partial pressures keep the makeup of the dissolved gasses constant.


No, that is very incorrect :D Often partial pressures are not met. For example, in a FW water tank high in fish, the partial pressure will be quite high for CO2, but it will really not reach equilibrium with the atmosphere, as the CO2 can not escape fast enough. This can cause a very low pH. The O2 will not change at all. Same for a lack of CO2, were plants remove the CO2 faster than it can enter the water, from a higher CO2 pressure in the air. It is the reason behind using OC2 injection in FW planted tanks. If there is not enough CO2 in solution, as the plants are uptaking it, the plants feed off the carbonates in the water and covert it to CO2, which raises the pH. The O2 will increase but it is due to the plants giving it off.

I always thought (ok, hoped ) that water movement was enough to keep DO levels higher at night - but I was curious, that's why I started the thread.

It can in many system, it depends on then load. That is, keeping it high enough form them to do Ok, as long as there is not excessive CO2 build up, followed by a low pH.

With plant action consuming carbon dioxide and releasing oxygen, it would make sense that lower carbon dioxide meant higher oxygen.

It does but it is the plants doing it. If you take a sample of water high in CO2 and then blow it off with an airstone the O2 will increase, but this not because you removed the CO2. O2 enters the water easily with aeration, CO2 or not.

Whereas before I added macros to my system, the daytime ph had lowered to 7.4 and all new fish slowly deteriorated and after a couple of weeks started breathing heavy, developed white spots then died the third week.

Yes, the pH was to low, due to pH, which caused the blood to become acidic. Normally at night the O2 levels are lower also. Under theses types of conditions, the Bohr and Root Effect also start to go astray, lower the O2 in their blood even more, which makes the CO2 uptake even more dangerous. A Triple Whammy ;)

But also is it only locally the oxygen is supersaturated? Sounds like circulation would help.

More circulation would drive it off so as it is already 100 %, the O2 may become lower.

As I understand it the total pressure in the sum of the partial pressures

Yes, but is not that simple. O2 is easily increased in water via aeration, where as CO2 is easily drive off via aeration.

And just to make it worse boomer tells the wife about a do meter.

Well, did she listen :D Think of all the data you will get :lol: :D



Tatu, you said it on a nut shell :thumbsup:

BTW, the actual mechanism of gas transport from the atmosphere to water column is quite complicated (laminar boundary layers, diffusion coefficients, transfer velocities, viscosity etc. etc.) and when you insert gas injection into the picture

Yes, that is very correct :D

[beaslbob]

So bottom line is that (whatever the mechanism) my fish did much better because of the carbon dioxide consumption and oxygen generation by the action of the plant life.

[Boomer]

Bob, did I tell you I lived in Huntsville for almost a year at RSA. I think I did but don't remember :confused: EOD stuff

[beaslbob]

Originally posted by Boomer
Bob, did I tell you I lived in Huntsville for almost a year at RSA. I think I did but don't remember :confused: EOD stuff

I know the eod from you signature.

I am at redstone now. Working for army avaition here.

[tatuvaaj]

Here's an interesting article by Göran E. Nilsson and Sara Östlund-Nilsson that suggests that my concern about low DO levels at night might be unwarranted:

"HYPOXIA ON CORAL REEFS AND HYPOXIA TOLERANCE IN CORAL REEF FISH"
Part of the proceedings available here: http://water.montana.edu/symposium/proceedings/default.htm

Of course it is still possible (even likely?) that some animals we try to keep do not have as great hypoxia tolerance as the fishes examined.

[Randy Holmes-Farley]

Thanks, Tatu. :)

[simonh]

I've had a search around but can't find any logs on my hard disk from my IKS aquacomputer during the time I was measuring oxygen levels. Unfortunatley, the probe is dead (again) so I am unable to measure at the moment. From observation I do remember the variation during a normal cycle been quite uninteresting. About the most interesting observation was that leaving the skimmer off in the day you could increase daytime oxygen levels.

I also have a Pinpoint Oxygen meter which is okay but it's difficult to do much as it doesn't have any automatic logging.

I'll see next weekend if I'm able to hookup the Pinpoint probe onto the IKS in some way and do some recording. I also have air-pressure module so it corrects for the air pressure. It also includes a setting for fresh/saltwater although you aren't able to enter the specific salinity so I assume it's tables are working on a fixed S=35 (or similar) when saltwater is selected.

P.S. If you are looking for Hach gear in Europe then www.DrLange.de should be able to give your country distributor. I use Camlab in the UK.